I am an American who has spent a lot of time in Taiwan. Their 'family style' manners are the same as American family-style which I am guessing is the same as Canadian family-style. The rules seem to be:
1) Everyone gets at least one short at every dish.
2) If it is 'hosted', try a little of each dish unless there is a reason. In Taiwan, I usually told the people ordering, "I will not eat cucumbers, scallops, or something uncooked which was once living."
3) Taking 'more than your share', would only apply, if at all, to the most desirable dish. Even then, it would be OK after everyone had two chances.
Even if the chinese family style rules were different, it wouldn't matter. Unless it is something obvious, like sitting on a cushion on the floor/Japanese, or eating with your hands/Ethiopian, the rules are the rules were you live.
Since he insists on authentic chinese, I assume he has the traditional confusion about vegetarianism. In Taiwain, I have witnessed a version of this exchange several times,
Veg: I can't have the X beef dish because I am a vegetarian. I don't eat anything that was once alive.
Chi: You don't eat vegetables?
Veg: I eat vegetables, not animals.
Chi: (Confusing veg. with Hindu) Well, we'll order the X dish in Pork then.
Veg: I can't eat pork, either.
Chi: Ok, well then Chicken.
Veg: Nothing that was alive.
Chi: Shrimp, then? Even kids eat shrimp.
Veg: No, I don't eat Shrimp.
Chi: Ok, Fish. Everyone eats fish.
Veg: Not me.
I think in this case, the real problem was your mother. She was going to give you grief. Period.